Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$189.37	13.523%	$214.9785	$214.98	$215.00	$215.00
Purchase #2	$137.99	12.501%	$155.2401	$155.24	$155.25	$155.20
Purchase #3	$239.25	3.397%	$247.3773	$247.38	$247.40	$247.40
Purchase #4	$89.62	11.422%	$99.8564	$99.86	$99.85	$99.90
Purchase #5	$52.28	4.506%	$54.6357	$54.64	$54.65	$54.60
Purchase #6	$61.48	6.393%	$65.4104	$65.41	$65.40	$65.40
Purchase #7	$109.39	8.715%	$118.9233	$118.92	$118.90	$118.90
7 purchase totals =	$879.38		$956.4217	$956.43	$956.45	$956.40